A retardation film may be, for example, disposed at one or both sides of a liquid crystal cell so as to improve viewing angle characteristics of liquid crystal display devices (LCDs), as described in Japanese Patent Laid-open Publication No. 1996-321381. The retardation film may also be used in reflective LCDs or organic light emitting devices (OLEDs) to prevent reflection of external light and secure visibility.
Retardation films are divided into ½-wavelength or ¼-wavelength retardation films, depending on phase retardation. Conventional ½- or ¼-wavelength retardation films have a phase difference which varies according to their wavelengths. Therefore, the wavelength range at which the ½- or ¼-wavelength retardation films may exert action may be limited to a certain wavelength range. For example, a film that functions as a ¼-wavelength retardation film with respect to light with a 550 nm wavelength may not often function as the ¼-wavelength retardation film with respect to light with a 450 nm or 650 nm wavelength.